1. Field of the Invention
The present invention relates to an apparatus that is provided in a sewing machine for performing sewing using a looper thread and needle threads, such as a multi-thread chain stitch sewing machine and a covering chain stitch sewing machine, to prevent raveling of a seam at the end of sewing, and also relates to a ravel preventing method implemented using this apparatus.
2. Description of Related Art
In a multi-thread chain stitch sewing machine and a covering chain stitch sewing machine, loops of needle threads 6a and 6b and a looper thread 7 are intertwined in an inter-looping manner on the back side of sewn cloth, and a seam shown in FIG. 1A is formed. The seam formed in such a manner has the following problem. If an end of the looper thread 7 cut at the end of sewing is pulled as shown by an arrow in FIG. 1A, the looper thread 7 may slip out of the final loops 6c and 6d of the needle threads 6a and 6b, and may move consecutively toward the sewing start side and cause a ravel.
Conventionally, various kinds of methods for preventing such raveling and apparatuses for implementing such a method have been put into practice, and one example is the ravel preventing method and apparatus invented by the applicant of this application (see, for example, Japanese Patent No. 2879399). In this method and apparatus, there is provided a looper thread hanging hook for holding a looper thread, which is passed into the loops of needle threads by the advance of the looper, on the left advance end of the looper. After temporarily suspending sewing by bringing the looper into an advance state just before the end of sewing, the looper thread is put on the looper thread hanging hook. Then, after sewing for one stitch in this state, the needle threads and looper thread are cut.
According to this invention, as shown in FIG. 1B, there is formed a seam in which the looper thread 7 caught by the looper thread hanging hook is intertwined in an interlacing manner with the final loops 6c and 6d of the needle threads 6a and 6b formed before suspending the sewing. Since the looper thread 7 intertwined in such a manner will not slip out of the final loops 6c and 6d even when its end is pulled as shown by an arrow, it is possible to certainly prevent raveling of the seam at the stage of occurrence, and thus it is possible to provide a reliable ravel prevention effect. Moreover, the seam at the sewing end portion does not look differ from other portion as shown in FIG. 1B, and therefore does not deteriorate the appearance.
The ravel preventing method proposed in the publication of Japanese Patent No. 2879399 is an excellent method capable of certainly preventing raveling that may occur in the vicinity of the sewing end portion in a sewing machine, such as a multi-thread chain stitch sewing machine and a covering chain stitch sewing machine, which performs sewing using a looper thread and needle threads.
By the way, in an apparatus for implementing the above-mentioned ravel preventing method, the looper thread hanging hook for catching the looper thread is arranged on the rear side of a needle drop position, on the left advance end side of the looper that advances from the right to left side of the needle drop position, and advances or retreats in the forward and backward direction at this position to catch the looper thread on the rear side of the looper.